Old growth forest store more carbon than they release.
Worldwide, forests between 15 and 800 years old remove a net 1 billion metric tons of carbon dioxide from the atmosphere each year.
This study, which analyzed more than 500 forests worldwide, challenges the conventional wisdom that old growth forests give off as much carbon as they take in and are thus carbon neutral. The authors of this report argue that, based on this research, the Kyoto Protocol and other "Cap and Trade" systems for greenhouse gases should allow credits for protecting old growth forests.
However, these old growth forests around the world are not protected by international treaties and have been considered of no significance in the national "carbon budgets" as outlined in the Kyoto Protocol. That perspective was largely based on findings of a single study from the late 1960s which had become accepted theory, and scientists now say it needs to be changed.
"Carbon accounting rules for forests should give credit for leaving old growth forest intact," researchers from Oregon State University and several other institutions concluded in their report. "Much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed."
Northern Hemisphere Old Growth Forests
The analysis of 519 different plot studies found that about 15% of the forest land in the Northern Hemisphere is unmanaged primary forests with large amounts of old growth, and that rather than being irrelevant to the Earth's carbon budget, they may account for as much as 10 percent of the global net uptake of carbon dioxide.
Forests of 15 to 800 Years of Age
In forests anywhere between 15 and 800 years of age, the study said, the net carbon balance of the forest and soils is usually positive -- meaning they absorb more carbon dioxide than they release.
"If you are concerned about offsetting greenhouse gas emissions and look at old forests from nothing more than a carbon perspective, the best thing to do is leave them alone," said Beverly Law, professor of forest science at OSU and director of the AmeriFlux network, a group of 90 research sites in North and Central America that helps to monitor the current global "budget" of carbon dioxide.
The current data now makes it clear that carbon accumulation can continue in forests that are centuries old.
The creation of new forests, whether naturally or by humans, is often associated with disturbance to soil and the previous vegetation, resulting in decomposition that exceeds for some period the net primary productivity of re-growth.
Old growth forests, the study said, continue to sequester carbon for many centuries. And when individual trees die due to lightning, insects, fungal attack or other causes, there is generally a second canopy layer waiting in the shade to take over and maintain productivity.
Offset Greenhouse gas Emissions with Intact Forests
One implication of the study, Law said, is that nations with significant amounts of old forests may find it somewhat easier to offset greenhouse gas emissions if those forests are left intact. It will also be necessary for land surface models that attempt to define carbon balance to better characterize function of old forests.
Many of the conclusions from the study were based on data acquired from the AmeriFlux and CarboEurope programs, researchers said.
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